In order to electronically generate musical sound with high fidelity, the recent trend in electronic piano is such a method in which samples of acoustically generated sound are stored in the form of PCM waveform data in memory of the electronic piano. In such electronic piano, sound is created by reading out the PCM waveform data. However, this method has a drawback: a massive amount of storage area is required for storing the PCM waveform data for each and every key of the piano and with respect to each key stroke intensity.
It is widely known that sound generated by the acoustic piano is composed of a plurality of harmonics. It is also known that any sound waveform can be created by synthesizing a plurality of sine waves. There leads to the method of generating sound by synthesizing sine waves of a plurality of harmonics.
By adopting this method, the data storage amount that has to be allocated for generating sound of all the piano keys and respective key stroke intensity is minimized and storage capacity of the memory is saved.
Meanwhile, when frequency analysis is conducted on the instantaneous frequency of the tone of the acoustic piano, a frequency spectrum corresponding to a plurality of harmonics is obtained, as shown in FIGS. 2A and 2B. The inventor of the present invention examined such frequency spectrum in every predetermined time period. When the harmonics included in the frequency spectrum were assorted on a time chart, it turned out that some of these harmonics have envelope curves of relatively smooth declination as shown in FIG. 3A, while other harmonics have swing (volume fluctuation) on their declining envelope curves as shown in FIG. 3B. Taking this into consideration, the inventor concluded that some harmonics among those to be synthesized need swing on their envelope curves in order to perfectly imitate sound of the acoustic instruments.
The prior art device or system generates musical sound by synthesizing sine waves of a plurality of harmonics. The prior art device or system, however, disregards the above described swing of envelope curve of harmonics and results in generating poor sounds. Although it has been devised to give swing to the whole sound created from synthesized sine waves and generates tremolo or vibrato sound, sound generated without tremolo or vibrato is still a plain sound lacking in richness. It was impossible to imitate complex and profound genuine sound of piano, violin and other acoustic instruments.